The invention relates to a vacuum pump, in particular a pump of the rotary-piston or Roots type.
Vacuum pumps comprise pump elements which are arranged in a suction chamber and, in case of rotary-piston pumps, are provided in the form of two rotary pistons. By rotation of the rotary pistons, the medium which is to be pumped will be conveyed from a suction side of a suction chamber to a pressure side. The conveying capacity of rotary-piston pumps is limited particularly by a maximal pressure difference between the suction side and the pressure side. In rotary-piston pumps having a pumping chamber with a large volume, this maximal pressure difference will be about 50 mbar, and in smaller rotary-piston pumps, it will be about 80 mbar. Should the maximal pressure difference be exceeded, this may happen to cause a thermal overstressing of the rotary-piston pump, particularly of the drive motor. To avoid the occurrence of such overstressing, some rotary-piston pumps comprise a connection channel connecting the pressure side to the suction side, allowing the conveyed medium to flow back from the pressure side to the suction side. Arranged in said connection channel is a valve, the so-called bypass line valve. At the point when a predetermined pressure difference has been reached, this usually weight- and/or spring-loaded valve will open.
Such a valve arranged in the connection channel of a rotary-piston pump is known e.g. from U.S. Pat. No. 4,470,767. Said valve is a disk valve comprising a disk-shaped valve body for closing a passage opening in the connection channel.
In modern production processes such as, e.g., vacuum coating processes, very short process times have to be achieved. For instance, it is required to realize cycle times of less than a minute. As a consequence, the vacuum pumps used in such processes, which particularly will be rotary-piston pumps, are required to perform the whole operating cycle of the pump within merely a few seconds. This has the consequence that the bypass line valve will be opened very quickly or abruptly. Due to the impacting of the valve disk or of components connected to the valves, increased operating noises will be generated. Further, such impacts may cause damage to the pump housing. In an effort to avoid such damage and to reduce operating noises, special valves have been developed wherein the valve disk is not only spring-loaded but additionally is provided with a hydraulic damper. Thereby, the quick or abrupt movement of the valve disk will be dampened.
Disk valves with or without hydraulic or mechanical damping have the dis-advantage that large masses must be moved. Consequently, disk valves are sluggish in operation. Particularly in rotary-piston valves having a large volume, it is required to provide correspondingly large valve disks for allowing a sufficient quantity of medium to flow back through the connection channel within a short time. A further disadvantage includes the large space requirement of the disk valve. This leads to bulky sizes of the pump houses and thus to increased costs. A further disadvantage of spring- and weight-loaded disk valves is the need, because of the gravitational acceleration, to give consideration to the mounting position. A special orientation of the disk valve at an angle of 45° relative to the conveying direction of the rotary-piston pump is known from U.S. Pat. No. 4,470,767. Thereby, it is possible to install the rotary-piston pump in least in two different mounting positions in which the disk valve is always arranged at an angle of 45° relative to the gravitational acceleration.
It is an object of the invention to provide a vacuum pump, in particular a pump of the type with rotary-pistons, by which shorter process times can be accomplished in modern production processes.
Also the vacuum pump of the invention, which particularly is a pump of the type with rotary-pistons, comprises a valve arranged in the connection channel between the pressure side and the suction side. Said valve comprises a spring-loaded valve body closing a passage opening of the connection channel, wherein, when a maximal pressure difference between the pressure side and the suction side is exceeded, the valve will be opened, in particular automatically. According to the invention, said valve body is formed as a pivotable valve flap. This has the particular advantage that the mass which has to be moved can be considerably reduced. It is thus made possible to not only realize a faster opening process but also, particularly, to achieve a considerable reduction of the noise development during the opening of the valve. Possible damage to the pump housing as might be caused when opening the valve, is thus avoided. By the provision of a flap valve instead of a disk valve, the invention makes it possible to realize shorter process times. A further considerable advantage of the invention resides in the potential for a distinct reduction of the constructional space, which is accomplished because the provision of a valve flap obviates the need for a cylindrical housing projection for arranging the disk valve therein. Instead, it is now possible to arrange the flap valve e.g. in a corner region of the housing so that the outer dimensions of the pump housing can be distinctly reduced.
Further, the geometric shape of the valve flap can be selected freely as desired. No need exists for a round passage opening arranged in the connection channel and closed by a round valve plate. Instead, according to a particularly preferred embodiment of the invention, the passage opening in the connection channel has a substantially rectangular and/or longitudinal shape. Particularly, the passage opening can extend substantially along the whole width of the connection channel. Preferably, herein, the connection channel is guided along the housing of the pumping chamber and extends substantially across the whole width of the pump housing and respectively the pumping chamber. In dependence on the pumping volume of the rotary-piston pump, the minimum cross section of the connection channel has to be defined to the effect that, upon occurrence of a load, a sufficient quantity of conveyed medium can be returned via the connection channel to the suction side. By the provision of a preferably rectangular valve flap, substantially the whole cross section of the connection channel can be opened when the maximum pressure difference is exceeded. This is not possible if disk valves are provided.
Since the process of opening the flap valve involves a pivoting of the valve flap about the rotary axis but not—in contrast to disk valves—a displacement of the whole valve disk, the masses which have to be moved are considerably smaller. Separate hydraulic or pneumatic damping is not required, even though it can be provided in special applications. Further, the valve body, when opened, will assume an orientation parallel to the flow direction so that an abutting impact will be avoided.
Since the mass of the moved components in a flap valve is small and is distributed such that, as provided by a particularly preferred embodiment of the invention, the gravitational center of the valve flap is located in the region of the pivot axis, the response behavior of the flap valve is independent of the mounting position of the rotary-piston pump. For the design of the system, this is of considerable advantage because the mounting positions of the rotary-piston pump are not restricted to only two positions as described in U.S. Pat. No. 4,470,767. Instead, the invention offers the special advantage that the position and the orientation of the valve within the pump are freely selectable. This allows for a reduction of the constructional space.
The pivot axis of the valve flap is preferably arranged on a side facing away from the pumping chamber. Preferably, the pivot axis of the valve flap extends parallel to rotary axes of the pump elements which in a rotary-piston pump are formed as rotary pistons. Thus, it is made possible that the pivot axis extends across the whole width of the pump housing. Particularly by the arrangement of the pivot axis on the side of the connection channel facing away from the pumping chamber, the pivot axis can now be arranged in a corner or an edge region of the pump housing. In this manner, the constructional space required for the flap valve can be considerably reduced, thus allowing for distinctly smaller outer dimensions of the pump housing than would be the case if corresponding disk valves were provided.
The pivot axis does not necessarily have to be a physical shaft or axis. Instead, it can also be a virtual axis. For instance, the pivot axis can also be realized in the form of a living hinge or the like. Further, it is possible to produce the valve flap from an elastic material at least in the region of the pivot axis so that, when the valve flap is being opened, the flap will be elastically deformed or bent in this region.
Further, the valve body can have a two-part design, the two parts preferably being configured in the manner of a swing door and preferably comprising respectively one pivot axis, with said pivot axes being arranged opposite to each other.
Further, it can be provided that said one or two pivot axes are arranged within the flow channel so that a fully opened valve flap will be arranged within the connection channel and be oriented in the flow direction. Thereby, depending on the given case, the constructional space may be still further reduced.